1. Field of the Invention
The present invention relates to the field of network management technologies. In particular, the present invention relates to the election of a master router in a redundant router protocol by tracking external events.
2. Background Information and Description of Related Art
The use of standby routers in an Internet Protocol (IP) network is known in the art. The Internet Engineering Task Force (IETF) has published a draft standard protocol for using standby routers, also referred to as redundant routers, entitled Virtual Router Redundancy Protocol, version 2-05, on Jan. 5, 2000 (VRRP).
In a typical network configuration, end-hosts that are connected to a layer-2 domain communicate with other subnets through the use of a default router. Often, the default router is statically configured as it minimizes configuration and processing overhead on the end-host and is widely supported by most Internet Protocol (IP) networks. As noted by the IETF, one of the drawback s of using a, statically configured default router is that it creates a single point of failure. Therefore, loss of the default router results in a catastrophic event, isolating all end-hosts that are unable to detect any alternate path that may be available. The use of standby routers (redundant routers) eliminates the single point of failure inherent in the static default routed environment. (VRRP, Section 1, Introduction).
Protocols for using standby routers involve the notion of a virtual router. A virtual router is an abstract object managed by a standby router protocol (SRP), and it functions as a default router for end-hosts on a network. The virtual router is defined by a Virtual Router Identifier (VRID) and a set of associated IP addresses. The virtual router may be implemented with two or more routers running the SRP. The SRP specifies an election process whereby the responsibility for forwarding packets sent to the IP address(es) associated with the virtual router is dynamically assigned to one of the SRP routers, called the master. The remaining SRP routers are referred to as backup or slave routers, and are available to assume forwarding responsibility for a virtual router should the current master fail.
Under the IETF's VRRP, the election process is based on the relative value of the priority field reported for each SRP router for a given VRID. The priority field may be an 8-bit unsigned integer field as set forth in the IETF's VRRP, Section 5.3.4. Higher values equal higher priority. The value of the priority field reported for the SRP router that owns the IP address(es) for a given VRID, i.e. the master SRP router, is always the highest priority value of 255. The value of the priority field reported for the backup SRP router(s) is a value from 1 to 254. The default priority field for a backup SRP router is 100. A value of zero in the priority field has a special meaning, and indicates that the SRP router has stopped participating in the SRP. This triggers the SRP backup router(s) to quickly elect one of among them transition to master status without waiting for the current master to timeout.
The determination of a priority for a particular SRP router may vary widely depending on the election process of the particular protocol in use and the policies set by network management. The efficiency of the transition from backup to master will depend in large part on how those priorities are determined. It would be desirable, therefore, to devise an SRP election process that takes into account a large number of operation scenarios such that the transition is as smooth and efficient as possible, and avoids erroneously electing a master SRP router that cannot communicate with the outside world.